It is well recognized that alcohol, medications and legal and illegal drugs can impair a person's ability to safely operate a vehicle. To address impairments resulting from alcohol intoxication, devices such as ignition interlock devices have been developed that require drivers to perform various actions before the vehicle's ignition system will operate. Current devices are considered active driver impairment detection devices because the devices require substantive actions by the driver to initiate and/or operate the systems. For example, many current devices require the driver to insert a tube into the driver's mouth and exhale a breath into the tube so that the device can detect the blood alcohol content of the driver. Ignition interlock devices are typically used when a driver has been convicted of a crime involving prior operation of a vehicle while impaired. Although use of the devices is inconvenient for the driver, the inconvenience is considered to be a reasonable part of the punishment for the crime committed by the driver.
In recent years, interest has grown in a passive driver impairment detection system that that could be used as standard equipment in vehicles to guard against impaired driving by the general population (i.e. including the vast majority of drivers who have not been convicted of crimes resulting from impaired driving). It is desirable to develop a driver impairment detection system that can detect driver impairments with little or no action by the driver to initiate or operate the system and thereby minimize any inconvenience to drivers and spur wide scale adoption and use of the system. Unfortunately, passive driver impairment detection systems that have been developed to date suffer from several deficiencies. The systems rely on lasers that require a relatively significant amount of time after power is first delivered to reach an operational stage. The systems therefore continue to be inconvenient for drivers. The systems may also power down and become inactive in situations where it would be desirable to maintain an active state (e.g., while a vehicle is temporarily stopped to allow a driver to watch an event from the vehicle).